Methods of forming hardfacing materials including PCD particles, and welding rods including such PCD particles

ABSTRACT

Methods of forming a hardfacing material include subjecting diamond grains to elevated temperatures and pressures to form diamond-to-diamond bonds between the diamond grains and form a PCD material. The PCD material is broken down to form PCD particles that include a plurality of inter-bonded diamond grains.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.12/497,420, filed Jul. 2, 2009, now U.S. Pat. No. 8,079,428, issued Dec.20, 2011, the disclosure of which is hereby incorporated herein by thisreference in its entirety.

TECHNICAL FIELD

Embodiments of the present invention relate to materials that may beused to increase the wear-resistance of earth-boring tools andcomponents of earth-boring tools used in the formation of wellbores, andto methods of forming and using such materials, tools, and components.

BACKGROUND

Wellbores are formed in subterranean formations for various purposesincluding, for example, extraction of oil and gas from subterraneanformations and extraction of geothermal heat from subterraneanformations. A wellbore may be formed in a subterranean formation usingan earth-boring rotary drill bit. Different types of earth-boring rotarydrill bits are known in the art including, for example, fixed-cutterdrill bits (which are often referred to in the art as “drag” bits),roller cone drill bits (which are often referred to in the art as “rock”bits), diamond-impregnated bits, and hybrid bits (which may include, forexample, both fixed cutters and roller cone cutters). The drill bit isrotated under an applied axial force, termed “weight-on-bit” (WOB) inthe art, and advanced into the subterranean formation. As the drill bitrotates, the cutters or abrasive structures thereof cut, crush, shear,and/or abrade away the formation material to form the wellbore.

The drill bit is coupled, either directly or indirectly, to an end ofwhat is referred to in the art as a “drill string,” which comprises aseries of elongated tubular segments connected end-to-end that extendsinto the wellbore from the surface of the formation. Various tools andcomponents, including the drill bit, may be coupled together at thedistal end of the drill string at the bottom of the wellbore beingdrilled. This assembly of tools and components is referred to in the artas a “bottom-hole assembly” (BHA).

The drill bit may be rotated within the wellbore by rotating the drillstring from the surface of the formation, or the drill bit may berotated by coupling the drill bit to a downhole motor, which is alsocoupled to the drill string and disposed proximate the bottom of thewellbore. The downhole motor may comprise, for example, a hydraulicMoineau-type motor having a shaft, to which the drill bit is coupled.The shaft of the motor is rotated by pumping fluid (e.g., drilling mudor fluid) from the surface of the formation down through the center ofthe drill string, through the hydraulic motor, out from nozzles in thedrill bit, and back up to the surface of the formation through theannular space between the outer surface of the drill string and theexposed surface of the formation within the wellbore.

The materials of earth-boring tools need to be relatively hard andwear-resistant to efficiently remove formation material within awellbore without undergoing excessive wear. Due to the extreme forcesand stresses to which drill bits and other earth-boring tools aresubjected during drilling and reaming operations, the materials ofearth-boring tools must simultaneously exhibit relatively high fracturetoughness. Materials that exhibit extremely high hardness, however, tendto be relatively brittle and do not exhibit high fracture toughness,while materials that exhibit high fracture toughness tend to berelatively soft and do not exhibit high hardness. As a result, acompromise must be made between hardness and fracture toughness whenselecting materials for use in drill bits.

In an effort to simultaneously improve both the hardness and fracturetoughness of earth-boring drill bits, composite materials have beenapplied to the surfaces of drill bits that are subjected to abrasion,erosion, or to both abrasion and erosion. These composite materials areoften referred to as “hardfacing” materials. Hardfacing materialstypically include at least one phase that exhibits relatively highhardness and another phase that exhibits relatively high fracturetoughness.

For example, hardfacing materials often include tungsten carbideparticles dispersed throughout a metal or metal alloy matrix material.The tungsten carbide particles are relatively hard compared to thematrix material, and the matrix material is relatively tough compared tothe tungsten carbide particles.

Tungsten carbide particles used in hardfacing materials may comprise oneor more of cast tungsten carbide particles, sintered tungsten carbideparticles, and macrocrystalline tungsten carbide particles. The tungstencarbide system includes two stoichiometric compounds, WC and W₂C, with acontinuous range of compositions therebetween. Cast tungsten carbidegenerally includes a eutectic mixture of the WC and W₂C compounds.Sintered tungsten carbide particles include relatively smaller particlesof WC bonded together by a matrix material. Cobalt and cobalt alloys areoften used as matrix materials in sintered tungsten carbide particles.Sintered tungsten carbide particles can be formed by mixing together afirst powder that includes the relatively smaller tungsten carbideparticles and a second powder that includes cobalt particles. The powdermixture is formed in a “green” state. The green powder mixture then issintered at a temperature near the melting temperature of the cobaltparticles to form a matrix of cobalt material surrounding the tungstencarbide particles to form particles of sintered tungsten carbide.Finally, macrocrystalline tungsten carbide particles generally consistof single crystals of WC.

Various techniques known in the art may be used to apply a hardfacingmaterial to a surface of an earth-boring tool. For example, automatedand manual welding processes may be used to apply hardfacing material toan earth-boring tool. In some manual processes, a welding rod thatcomprises the hardfacing material is provided, and a torch (e.g., anoxyacetylene torch or an arc-welding torch) is used to heat an end ofthe rod and, optionally, the surface of the tool to which the hardfacingis to be applied. The end of the rod is heated until at least the matrixmaterial begins to melt. As the matrix material at the end of the rodbegins to melt, the melting hardfacing material is applied to thesurface of the tool. The hard particles dispersed within the matrixmaterial are also applied to the surface with the molten matrixmaterial. After application, the molten matrix material is allowed tocool and solidify.

Such welding rods may comprise a substantially solid, cast rod of thehardfacing material, or they may comprise a hollow, cylindrical tubeformed from the matrix material of the hardfacing material and filledwith hard particles (e.g., tungsten carbide particles). In welding rodsof the tubular configuration, at least one end of the hollow,cylindrical tube may be sealed. The sealed end of the tube then may bemelted or welded onto the desired surface on the earth-boring tool. Asthe tube melts, the tungsten carbide particles within the hollow,cylindrical tube mix with the molten matrix material as it is depositedonto the surface of the tool. An alternative technique involves forminga cast rod of the hardfacing material.

Flame spray processes are also used to apply hardfacing materials toearth-boring tools. In a flame spray process, a powder comprising thehard particles and particles of the matrix material is carried by apressurized fluid (e.g., a pressurized gas) to a nozzle. The powdermixture is sprayed out from the nozzle and through a flame toward thesurface of the tool to which the hardfacing is to be applied. The flamecauses the particles of matrix material to at least partially melt. Asthe material is sprayed onto the tool, the molten matrix material coolsand solidifies, and the hard particles become embedded in the matrixmaterial to form the hardfacing on the surface of the tool.

Various types of arc welding processes are known in the art and may beused to apply hardfacing to a surface of an earth-boring tool. Forexample, metal-inert gas (MIG) welding processes, tungsten-inert gas(TIG) welding processes, and plasma-transferred arc (PTA) weldingprocesses may be used to apply hardfacing to a surface of anearth-boring tool.

There remains a need in the art for abrasive, wear-resistant hardfacingmaterials that exhibit improved resistance to abrasion, erosion, or bothabrasion and erosion.

BRIEF SUMMARY OF THE INVENTION

In some embodiments, the present invention includes hardfacing materialscomprising particles of polycrystalline diamond material embedded withina matrix material. The particles of polycrystalline diamond materialcomprise a plurality of inter-bonded diamond grains.

In additional embodiments, the present invention includes materialcompositions and structures, such as welding rods, that may be used toapply a hardfacing material to a surface of an earth-boring tool. Thematerial compositions and structures include particles ofpolycrystalline diamond material comprising a plurality of inter-bondeddiamond grains. For example, a welding rod may comprise an elongated,generally cylindrical body comprising a metal matrix material, andparticles of polycrystalline diamond material carried by the elongated,generally cylindrical body.

In additional embodiments, the present invention includes earth-boringtools that include a body, at least one cutting element on the body, anda hardfacing material on at least a portion of a surface of the body.The hardfacing material includes particles of polycrystalline diamondmaterial embedded within a matrix material. The particles ofpolycrystalline diamond material include a plurality of inter-bondeddiamond grains.

In further embodiments, the present invention includes methods of foilling a hardfacing material in which diamond grains are subjected to atemperature greater than about 1,500° C. and a pressure greater thanabout 5.0 gigapascals (GPa) to form diamond-to-diamond bonds between thediamond grains and form a polycrystalline diamond material. Thepolycrystalline diamond material is broken down to form particles ofpolycrystalline diamond material that include a plurality ofinter-bonded diamond grains.

Yet further embodiments of the present invention include methods ofhardfacing an earth-boring tool in which particles of polycrystallinediamond material that include a plurality of inter-bonded diamond grainsare bonded to a surface of an earth-boring tool using a metal matrixmaterial.

BRIEF DESCRIPTION OF THE DRAWINGS

While the specification concludes with claims particularly pointing outand distinctly claiming that which is regarded as the present invention,various features and advantages of embodiments of this invention may bemore readily ascertained from the following description of someembodiments of the invention when read in conjunction with theaccompanying drawings, in which:

FIG. 1 is a simplified drawing of an embodiment of a hardfacing materialof the present invention;

FIG. 2A is a simplified drawing of a hard particle of the hardfacingmaterial of FIG. 1 that includes polycrystalline diamond material;

FIG. 2B is a cross-sectional view of the hard particle shown in FIG. 2Ataken along section line 2B-2B therein;

FIG. 2C is a simplified sketch showing how the hard particle of FIGS. 2Aand 2B may appear under magnification, and illustrates a plurality ofinter-bonded diamond grains;

FIG. 3 is a partially cut-away view of a cutting element that includes alayer of polycrystalline diamond material that may be used to form hardparticles like that shown in FIGS. 2A-2C;

FIG. 4 is a partially cut-away view of the layer of polycrystallinediamond material shown in FIG. 3 removed from a substrate on which thelayer was previously disposed;

FIG. 5 is a perspective view of an embodiment of a welding rod of thepresent invention that includes hard particles like that shown in FIGS.2A-2C;

FIG. 6A is a perspective view of another embodiment of a welding rod ofthe present invention that includes hard particles like that shown inFIGS. 2A-2C;

FIG. 6B is a longitudinal cross-sectional view of the welding rod shownin FIG. 6A;

FIG. 7 is a side view of an embodiment of a roller cone earth-boringrotary drill bit of the present invention that includes a hardfacingmaterial like that shown in FIG. 1; and

FIG. 8 is a perspective view of an embodiment of a fixed-cutterearth-boring rotary drill bit of the present invention that includes ahardfacing material like that shown in FIG. 1.

DETAILED DESCRIPTION

The illustrations presented herein are not actual views of anyparticular drilling system, drilling tool assembly, or component of suchan assembly, but are merely idealized representations which are employedto describe the present invention.

As used herein, the term “polycrystalline diamond material” means andincludes a volume of material that includes two or more grains (alsoreferred to in the art as “crystals”) bonded directly to one another atleast partially by diamond-to-diamond bonds. In other words,polycrystalline diamond material is a material that includes two or moreinter-bonded diamond grains.

As used herein, the term “inter-bonded diamond grains” means grains thatare directly bonded to one another at least partially bydiamond-to-diamond bonds.

FIG. 1 is a simplified drawing illustrating an embodiment of ahardfacing material 10 of the present invention. The hardfacing material10 comprises a composite material that includes a discontinuous or“dispersed” phase 12 embedded within and dispersed throughout acontinuous matrix phase 14. The discontinuous phase 12 exhibits ahardness higher than a hardness exhibited by the matrix phase 14, andthe matrix phase 14 exhibits a fracture toughness higher than a fracturetoughness exhibited by the discontinuous phase 12.

The matrix phase 14 of the hardfacing material 10 may comprise a metalor metal alloy. By way of example and not limitation, the matrix phase14 may comprise cobalt-based, iron-based, nickel-based, iron- andnickel-based, cobalt- and nickel-based, iron- and cobalt-based,copper-based, and titanium-based alloys. The matrix phase 14 may also beselected from commercially pure elements such as cobalt, iron, nickel,copper, and titanium. In some embodiments, the matrix phase 14 maycomprise a matrix or “binder” material having a melting point belowabout 1,350° C., as disclosed in U.S. Patent Application Publication No.2005/0247491 A1, filed Apr. 28, 2005, and entitled “Earth-Boring Bits,”the entire disclosure of which is incorporated herein in its entirety bythis reference.

The discontinuous phase 12 may comprise finite spatial volumes ofpolycrystalline diamond material that are dispersed throughout andembedded within the matrix phase 14. In some embodiments, the finitespatial volumes of the discontinuous phase 12 may be formed from andcomprise particles of polycrystalline diamond (PCD) material, which arehereinafter referred to as PCD particles.

The hardfacing material 10 optionally may also comprise an additionaldiscontinuous phase 13 that includes at least one of a carbide material(e.g., tungsten carbide, titanium carbide, tantalum carbide, siliconcarbide, etc.), a boride material (e.g., titanium boride), a nitridematerial (e.g., silicon nitride), and non-polycrystalline diamond grit.

The hardfacing material 10 may be applied to surfaces of earth-boringtools using various methods. For example, automated and manual weldingprocesses may be used to apply hardfacing material 10 to a surface of anearth-boring tool. Various types of arc welding processes may be used toapply hardfacing material 10 to a surface of an earth-boring tool. Forexample, metal-inert gas (MIG) welding processes, tungsten-inert gas(TIG) welding processes, and plasma-transferred arc (PTA) weldingprocesses may be used to apply hardfacing material 10 to a surface of anearth-boring tool. Flame spray processes also may be used to applyhardfacing material 10 to surfaces of earth-boring tools.

FIGS. 2A-2C illustrate an example of a PCD particle 16 that may be usedin accordance with embodiments of the present invention to form thediscontinuous phase 12 of the hardfacing material 10 of FIG. 1.

Referring to FIG. 2A, the PCD particles 16 used to form the hardfacingmaterial 10 (FIG. 1) may have irregular rough and jagged shapes in someembodiments of the present invention. In other words, the PCD particles16 may comprise relatively sharp edges and corners. In additionalembodiments of the present invention, the PCD particles 16 may berelatively smooth and rounded. Relatively rough and jagged PCD particles16 may be processed to form relatively smooth and rounded PCD particlesusing processes known in the art, such as, for example, tumblingprocesses, jet blending processes, and etching processes. Depending onthe particular application for which the hardfacing material 10 (FIG. 1)is to be used, either relatively rough and jagged PCD particles 16, asshown in FIG. 2A, or relatively smooth and rounded PCD particles mayexhibit more desirable physical characteristics and performance.

FIG. 2B is a cross-sectional view of the PCD particle 16 of FIG. 2Ataken along section line 2B-2B therein. As shown in FIG. 2B, in someembodiments of the present invention, the PCD particles 16 used to formthe discontinuous phase 12 of the hardfacing material 10 (FIG. 1) may beat least substantially planar. In other embodiments, however, the PCDparticles 16 may not be planar, and may be generally spherical, cubical,etc.

In embodiments in which the PCD particles 16 are at least substantiallyplanar as shown in FIGS. 2A and 2B, the PCD particles 16 may have anaverage particle diameter D of, for example, between about 0.25millimeter and about 7.0 millimeters, and an average thickness T of, forexample, between about 0.1 millimeter and about 5.0 millimeters.

As shown in FIG. 2B, in some embodiments, the PCD particles 16 may be atleast partially encapsulated with a coating 17 prior to forming ahardfacing material 10 using the PCD particles 16. The coating 17 may beused to protect the polycrystalline diamond material within the PCDparticles 16 against thermal degradation (e.g., graphitization) thatmight occur during formation of a hardfacing material 10 using the PCDparticles 16. By way of example and not limitation, the coating 17 maycomprise a powder material comprising particles of a metal or metalalloy material that does not serve as a catalyst material for catalyzingthe formation of diamond-to-diamond bonds at elevated temperatures andpressures, as described in further detail below. Such catalyst materialsmay, conversely, contribute to the thermal degradation of diamondmaterial when the diamond material and the catalyst are heated torelatively lower temperatures and pressures. For example, the coating 17may comprise particles of tungsten metal or a tungsten metal alloy. Thecoating 17 also may comprise particles of at least one of a carbidematerial (e.g., tungsten carbide, titanium carbide, tantalum carbide,silicon carbide, etc.), a boride material (e.g., titanium boride), anitride material (e.g., silicon nitride), and non-polycrystallinediamond grit. Such a powder coating 17 optionally may be subjected to asintering process to at least partially sinter particles within thepowder coating 17. By way of non-limiting example, the PCD particles 16may be coated using methods such as those disclosed in U.S. Pat. No.7,350,599, which issued Apr. 1, 2008 to Lockwood et al., the entiredisclosure of which is incorporated herein by this reference.

In additional embodiments, the coating 17 may comprise a layer of one ormore of the above-mentioned coating materials deposited by, for example,using a physical vapor deposition (PVD) process or a chemical vapordeposition (CVD) process.

As previously mentioned, the PCD particles 16 may comprise a pluralityof inter-bonded diamond grains. FIG. 2C is a simplified drawingillustrating how the microstructure of the PCD particles 16 may appearat a magnification of between about 500 times and about 1,500 times.

FIG. 2C illustrates a plurality of inter-bonded diamond grains 18, 18′.The diamond grains 18, 18′ may have an average particle size within arange extending from about five microns (5.0 μm) to about thirty microns(30.0 μm). In some embodiments, the diamond grains 18, 18′ may have amulti-modal grain size distribution. In other words, the diamond grains18, 18′ may comprise a mixture of two, three, or even more differentsizes of grains. For example, in the embodiment of FIG. 2C, theinter-bonded diamond grains 18, 18′ include both larger diamond grains18 and smaller diamond grains 18′. The larger and smaller diamond grains18, 18′ are bonded together by diamond-to-diamond bonds at grainboundaries between the diamond grains 18, 18′ (the grain boundariesbeing represented in FIG. 2C by dashed lines) to form thepolycrystalline diamond material of the PCD particles 16. In someembodiments, interstitial spaces 20 (shaded black in FIG. 2C) betweenthe inter-bonded diamond grains 18, 18′ may be filled with a catalystmaterial used to catalyze formation of the diamond-to-diamond bondsbetween the diamond grains 18, 18′. In other embodiments, however,catalyst material may be removed from the interstitial spaces 20 betweenthe inter-bonded diamond grains 18, 18′ such that the interstitialspaces 20 comprise voids, as discussed in further detail herein below.In such embodiments, the polycrystalline diamond material of the PCDparticles 16 may be porous, and a majority of the pores within the PCDparticles 16 may form a continuous open pore network within thepolycrystalline diamond material.

In some embodiments of the present invention, PCD particles 16 used inthe hardfacing material 10 (FIG. 1) may be formed by breaking down(e.g., crushing, milling, grinding, etc.) a relatively larger volume ofpolycrystalline diamond material. By way of example and not limitation,the PCD particles 16 may be formed by breaking down a layer ofpolycrystalline diamond material of a cutting element, which previouslymay have been disposed on a substrate. Thus, the PCD particles 16 maycomprise fragments of a layer of polycrystalline diamond material. Insome embodiments, such fragments may be at least substantially planar.

FIG. 3 illustrates a cutting element 30 like those often used on drillbits and reamers used to form wellbores in subterranean formations. Thecutting element 30 shown in FIG. 3 includes a volume of polycrystallinediamond material 32 bonded to a substrate 34. The volume ofpolycrystalline diamond material 32 is often referred to in the art as a“diamond table.” The volume of polycrystalline diamond material 32 maybe formed on the substrate 34, or the volume of polycrystalline diamondmaterial 32 may be formed separately from the substrate 34 andsubsequently attached to the substrate 34. As known in the art,polycrystalline diamond material may be formed by subjecting diamondgrains to elevated temperatures and pressures to form diamond-to-diamondbonds between the diamond grains. For example, polycrystalline diamondmaterial may be formed by subjecting diamond grains to temperaturesgreater than about 1,500° C. and pressures greater than about 5.0 GPa inthe presence of a catalyst material such as, for example, cobalt for atime of between about ten seconds and several minutes. The catalyst isused to catalyze formation of the diamond-to-diamond bonds between thediamond grains. Other suitable catalysts are also known in the art. Ifthe temperatures and pressures are sufficiently high (e.g., at atemperature greater than about 3,000° C. and a pressure greater thanabout 13.0 GPa), diamond-to-diamond bonds may form even in the absenceof a catalyst.

Referring to FIG. 4, the volume of polycrystalline diamond material 32may be removed from the substrate 34 of the cutting element 30. Thevolume of polycrystalline diamond material 32 may be removed from thesubstrate 34 using, for example, a wire Electrical Discharge Machining(EDM) process. Other processes, such as grinding processes, etchingprocesses, or fracturing processes, also may be used to separate thevolume of polycrystalline diamond material 32 and the substrate 34.After removing the volume of polycrystalline diamond material 32 fromthe substrate 34, the volume of polycrystalline diamond material 32 maybe broken down to form a plurality of PCD particles 16 (FIGS. 2A-2C)therefrom.

Thus, some embodiments of methods of the present invention includeforming a plurality of PCD particles 16 from a volume of polycrystallinediamond material 32 that was previously part of a cutting element 30. Asa result, in accordance with some embodiments of the present invention,cutting elements 30 (which may or may not have been previously used indrilling or reaming a wellbore) that would otherwise be discarded may besalvaged and recycled by using the cutting elements 30 to form PCDparticles 16 (FIGS. 2A-2C) for use in a hardfacing material 10 (FIG. 1).In additional embodiments of methods of the present invention, a volumeof polycrystalline diamond material 32 may be formed with the intentionof subsequently breaking down the volume of polycrystalline diamondmaterial 32 to form PCD particles 16 (FIGS. 2A-2C) for use in ahardfacing material 10 (FIG. 1).

After forming the PCD particles 16, the PCD particles 16 may optionallybe subjected to a leaching process to remove catalyst material frominterstitial spaces 20 between the inter-bonded diamond grains 18. Byway of example and not limitation, the PCD particles 16 may be leachedusing a leaching agent and process such as those described more fullyin, for example, U.S. Pat. No. 5,127,923 to Bunting et al. (issued Jul.7, 1992), and U.S. Pat. No. 4,224,380 to Bovenkerk et al. (issued Sep.23, 1980), the disclosure of each of which is incorporated herein in itsentirety by this reference. Specifically, aqua regia (a mixture ofconcentrated nitric acid (HNO₃) and concentrated hydrochloric acid(HCl)) may be used to at least substantially remove catalyst materialfrom the interstitial spaces 20 between the inter-bonded diamond grains18 in the PCD particles 16. It is also known to use boiling hydrochloricacid (HCl) and boiling hydrofluoric acid (HF) as leaching agents. Oneparticularly suitable leaching agent is hydrochloric acid (HCl) at atemperature of above 110° C., which may be provided in contact with thePCD particles 16 for a period of about two hours to about 60 hours,depending upon the size of the PCD particles 16. After leaching the PCDparticles 16, the interstitial spaces 20 between the plurality ofinter-bonded diamond grains 18 within the PCD particles 16 may be atleast substantially free of catalyst material used to catalyze formationof diamond-to-diamond bonds between the plurality of inter-bondeddiamond grains 18.

Additional embodiments of the present invention include materialcompositions and structures that may be used to form a hardfacingmaterial 10 on an earth-boring tool. Such material compositions andstructures also include PCD particles (such as the PCD particles 16 aspreviously described with reference to FIGS. 2A-2C), and may include amatrix material used to form a matrix phase 14 of hardfacing material10. By way of example and not limitation, the PCD particles 16 may beincorporated into a welding rod, and the welding rod may be used todeposit hardfacing material 10 on a surface of an earth-boring tool.

FIG. 5 is a simplified perspective view of an embodiment of a solidwelding rod 40 of the present invention. The solid welding rod 40 shownin FIG. 5 may comprise an at least substantially solid cylinder thatincludes PCD particles 16 embedded within a matrix material that willultimately form the matrix phase 14 of the hardfacing material 10 (FIG.1). Thus, the solid welding rod 40 includes an elongated, generallycylindrical body comprising the matrix material, and the PCD particles16 are carried by the body. As the matrix material of the welding rod 40will ultimately form the matrix phase 14 of the hardfacing material 10,the matrix material of the welding rod 40 may have a materialcomposition as previously described for the matrix phase 14 of thehardfacing material 10 of FIG. 1. The solid welding rod 40 may furthercomprise additional hard particles that include at least one of acarbide material (e.g., tungsten carbide, titanium carbide, tantalumcarbide, silicon carbide, etc.), a boride material (e.g., titaniumboride), a nitride material (e.g., silicon nitride), andnon-polycrystalline diamond grit. The solid welding rod 40 of FIG. 5 maybe formed using, for example, a forging process, a casting process, oran extrusion process.

FIG. 6A is a simplified perspective view of another embodiment of atubular welding rod 50 of the present invention. The tubular welding rod50 shown in FIG. 6A may comprise a generally hollow, cylindrical tube 52that is at least substantially comprised by a metal or metal alloy thatwill be used to form the matrix phase 14 of the hardfacing material 10(FIG. 1). Thus, the matrix material of the welding rod 50 may have amaterial composition as previously described for the matrix phase 14 ofthe hardfacing material 10 of FIG. 1. FIG. 6B is a longitudinalcross-sectional view of the tubular welding rod 50 of FIG. 6A. As shownin FIG. 6B, the interior space within the hollow, cylindrical tube 52may be filled with PCD particles 16. The tube 52 may also containadditional hard particles that include at least one of a carbidematerial (e.g., tungsten carbide, titanium carbide, tantalum carbide,silicon carbide, etc.), a boride material (e.g., titanium boride), anitride material (e.g., silicon nitride), and non-polycrystallinediamond grit. One or both ends of the tube 52 may be capped, crimped, orotherwise sealed to prevent the PCD particles 16 (and any other hardparticles therein) from falling out from the tube 52. Thus, the tubularwelding rod 50 also includes an elongated, generally cylindrical tubularbody comprising a matrix material (i.e., tube 52), and the PCD particles16 are carried by the body. The hollow, cylindrical tube 52 of thewelding rod 50 of FIGS. 6A and 6B may be formed using, for example, aforging process, a casting process, or an extrusion process.

Embodiments of welding rods of the present invention (e.g., the solidwelding rod 40 of FIG. 5 and the tubular welding rod 50 of FIGS. 6A and6B) may be used to apply hardfacing material 10 to a surface of anearth-boring tool using a torch such as, for example, an oxyacetylenetorch or an arc-welding torch. The torch is used to heat an end of thewelding rod and, optionally, the surface of the earth-boring tool towhich the hardfacing material is to be applied. An end of the weldingrod is heated until at least the matrix material in the welding rodbegins to melt. As the matrix material at the end of the welding rodbegins to melt, the melting matrix material, and PCD particles 16 fromthe welding rod that become entrained within the melting matrixmaterial, are applied to the surface of the earth-boring tool. Afterapplication, the molten matrix material is allowed to cool and solidifyon the surface of the earth-boring tool, the PCD particles 16 becomeembedded within the solidified matrix material. The resulting hardfacingmaterial 10 (FIG. 1) includes a continuous matrix phase 14, which isformed by the matrix material of the welding rod, and a discontinuousphase 12 comprising polycrystalline diamond material that is formed bythe PCD particles 16 of the welding rod.

Additional embodiments of the present invention include powder feedstockmixtures for use in flame spray processes that include PCD particles 16.For example, a powder feedstock mixture for a flame spray process maycomprise a mixture of PCD particles 16, as well as particles of a metalor metal alloy matrix material having a composition as previouslydescribed in relation to the matrix phase 14 of the hardfacing material10 (FIG. 1). The mixture may also comprise additional hard particlesthat include at least one of a carbide material (e.g., tungsten carbide,titanium carbide, tantalum carbide, silicon carbide, etc.), a boridematerial (e.g., titanium boride), a nitride material (e.g., siliconnitride), and non-polycrystalline diamond grit. In a flame sprayprocess, such a powder feedstock mixture may be entrained within andcarried by a pressurized fluid (e.g., a pressurized gas) to a flamespray nozzle. The pressurized fluid and the powder mixture may besprayed out from the nozzle and through a flame toward the surface ofthe earth-boring tool to which the hardfacing material 10 is to beapplied. The flame causes the particles of matrix material to at leastpartially melt. As the powder mixture is sprayed onto the tool, themolten matrix material cools and solidifies, and the PCD particles 16become embedded within the solidified matrix material. The resultinghardfacing material 10 (FIG. 1) includes a continuous matrix phase 14,which is formed by the particles of matrix material in the powderfeedstock mixture, and a discontinuous phase 12 comprisingpolycrystalline diamond material that is formed by the PCD particles 16in the powder feedstock mixture.

Additional embodiments of the present invention include earth-boringtools having a hardfacing material 10 (as previously described herein inrelation to FIG. 1 and including a discontinuous phase 12 comprisingfinite spatial volumes of polycrystalline diamond material dispersedwithin a matrix phase 14) on at least a portion of a surface of a bodyof the tools. The tools may also include at least one cutting element.By way of example and not limitation, earth-boring tools such as, forexample, fixed-cutter rotary drill bits, roller cone rotary drill bits,diamond impregnated rotary drill bits, reamer tools, mills, and coringbits may include hardfacing material 10 and may embody the presentinvention.

FIG. 7 illustrates an embodiment of a roller cone drill bit 60 of thepresent invention. The roller cone drill bit 60 includes a bit body 62having threads 64 at its proximal longitudinal end for connection to adrill string (not shown). The bit body 62 may comprise a plurality(e.g., three) of head sections 66 (which are separated by the dottedlines in FIG. 7) that are welded together concentrically about alongitudinal axis 67 of the drill bit 60. The threads 64 may be machinedin the conical shank region of the bit body 62 after welding togetherthe head sections 66. Two of the head sections 66 are visible from theperspective of FIG. 7.

Each head section 66 comprises a head section body or proximal section68 nearest the threads 64 and a bit leg 70 depending distally therefrom.Each proximal section 68 of the drill bit 60 may include a lubricantfluid pressure compensator 72, as known in the art. At least one nozzle74 may be provided in the bit body 62 for controlling the direction andvelocity of pressurized drilling fluid flowing through the bit body 62and out from the nozzle 74 during drilling operations. A roller conecutter 76 is rotatably secured to a bearing shaft (not shown) of eachrespective bit leg 70 of bit body 62. By way of example, the drill bit60 has three roller cone cutters 76, one of which is obscured from viewfrom the perspective of FIG. 7. Each roller cone cutter 76 has rows ofcutting elements 78. The cutting elements 78 may comprise cutting teeth,which may be machined in exterior surfaces of the bodies of the rollercone cutters 76. Alternatively, the cutting elements 78 may compriseseparately formed inserts, which may be formed from a wear-resistantmaterial such as cemented tungsten carbide and pressed into recessesdrilled or otherwise formed in exterior surfaces of the bodies of theroller cone cutters 76.

The roller cone drill bit 60 of FIG. 7 may include hardfacing material10 on one or more surfaces of the drill bit 60. By way of example andnot limitation, the outer surfaces of the head sections 66, includingexterior surfaces of both the proximal sections 68 of the head sections66 and the bit legs 70 of the head sections 66 may comprise hardfacingmaterial 10 thereon. Furthermore, hardfacing material 10 may be providedon various surfaces of the roller cone cutters 76. For example,hardfacing material 10 may be provided on gage surfaces 80 of the rollercone cutters 76, on the cutting elements 78 (e.g., on cutting teeth), oron both the gage surfaces 80 and on the cutting elements 78. Hardfacingmaterial 10 also may be applied to surfaces of the drill bit 60 withinthe fluid passageways (not shown) extending through the drill bit 60, aswell as to surfaces of the drill bit 60 proximate the nozzles 74, andother surfaces that might be susceptible to fluid erosion duringdrilling operations.

FIG. 8 illustrates an embodiment of a fixed-cutter drill bit 90 of thepresent invention. The fixed-cutter drill bit 90 includes a bit body 92having threads 94 at its proximal longitudinal end for connection to adrill string (not shown). The bit body 92 may comprise a crown 96, whichmay be formed from a particle-matrix composite material (e.g., acemented tungsten carbide material) or a metal alloy (e.g., steel). Thecrown 96 may be attached to a shank 97, and the threads 94 may bemachined in the shank 97.

The crown 96 of the drill bit 90 may comprise a plurality of blades 98that are separated from one another by fluid passageways 100. The blades98 may extend over the face of the crown 96 from a central cone regionof the crown 96 to a gage region of the crown 96. Radially outersurfaces of the blades 98 in the gage region of the crown 96 comprisegage surfaces 102 of the drill bit 90. These gage surfaces 102 definethe diameter of any wellbore drilled by the drill bit 90. The portionsof the fluid passageways 100 between the blades 98 in the gage region ofthe crown 96 are often referred to in the art as “junk slots.”

A plurality of cutting elements 104 may be fixedly attached to each ofthe blades 98. The cutting elements 104 may comprise, for example, PDCcutting elements. Fluid passageways (not shown) also extend through thedrill bit 90 to nozzles 106 to allow drilling fluid to be pumped throughthe drill string (not shown) and the drill bit 90 and out the nozzles106 during drilling operations.

The fixed-cutter drill bit 90 of FIG. 8 may include hardfacing material10 on one or more surfaces of the drill bit 90. By way of example andnot limitation, the gage surfaces 102 may comprise hardfacing material10 thereon. Furthermore, hardfacing material 10 may be provided onvarious formation-engaging surfaces of the blades 98. Hardfacingmaterial 10 also may be applied to surfaces of the drill bit 90 withinthe fluid passageways (not shown) extending through the drill bit 90, aswell as to surfaces of the drill bit 90 proximate the nozzles 106, andother surfaces that might be susceptible to fluid erosion duringdrilling operations.

Thus, surfaces of earth-boring tools such as, for example, the rollercone drill bit 60 of FIG. 7 and the fixed-cutter drill bit 90 of FIG. 8,may be hardfaced by bonding particles of polycrystalline diamondmaterial, such as the PCD particles 16 of FIGS. 2A-2C, to the surfacesusing a matrix material, which may comprise a metal or metal alloy, aspreviously described herein.

PCD particles 16, as previously described herein, may also be used inother components of earth-boring tools other than hardfacing material toprovide wear resistance to the earth-boring tools. As a non-limitingexample, PCD particles 16 may be disposed within bit bodies of so-called“diamond-impregnated” rotary drill bits such as those disclosed in, forexample, U.S. Pat. No. 6,843,333, which issued Jan. 18, 2005 to Richertet al., the entire disclosure of which is incorporated herein by thisreference.

The foregoing description is directed to particular embodiments for thepurpose of illustration and explanation. It will be apparent, however,to one skilled in the art that many modifications and changes to theembodiments set forth above are possible without departing from thescope of the embodiments disclosed herein as hereinafter claimed,including legal equivalents. It is intended that the following claims beinterpreted to embrace all such modifications and changes.

1. A method of forming a hardfacing material, comprising: subjectingdiamond grains to a temperature greater than about 1,500° C. and apressure greater than about 5.0 GPa to form diamond-to-diamond bondsbetween the diamond grains and form a polycrystalline diamond material;and breaking down the polycrystalline diamond material to form particlesof polycrystalline diamond material, the particles of polycrystallinediamond material comprising a plurality of inter-bonded diamond grains.2. The method of claim 1, wherein breaking down the polycrystallinediamond material comprises crushing the polycrystalline diamondmaterial.
 3. The method of claim 1, further comprising catalyzingformation of the diamond-to-diamond bonds between the diamond grainsusing a catalyst material.
 4. The method of claim 3, further comprisingremoving the catalyst material from interstitial spaces between theinter-bonded diamond grains within the particles of polycrystallinediamond material.
 5. The method of claim 1, further comprisingencapsulating the particles of polycrystalline diamond material with anencapsulant material comprising a metal.
 6. The method of claim 5,further comprising forming the encapsulant to further comprise at leastone of a carbide material, a boride material, a nitride material, andnon-polycrystalline diamond grit.
 7. The method of claim 1, furthercomprising embedding the particles of polycrystalline diamond materialwithin a matrix material.
 8. The method of claim 7, further comprisingforming the matrix material to comprise a metal.
 9. The method of claim8, further comprising forming the matrix material to comprise at leastone of a carbide material, a boride material, a nitride material, andnon-polycrystalline diamond grit.
 10. The method of claim 7, whereinembedding the particles of polycrystalline diamond material within thematrix material comprises embedding the particles of polycrystallinediamond material within the matrix material on a surface of anearth-boring tool.
 11. The method of claim 10, wherein embedding theparticles of polycrystalline diamond material within the matrix materialon the surface of the earth-boring tool comprises embedding theparticles of polycrystalline diamond material within the matrix materialon a surface of an earth-boring rotary drill bit.
 12. The method ofclaim 10, wherein embedding the particles of polycrystalline diamondmaterial within the matrix material on the surface of the earth-boringtool comprises: using a welding torch to at least partially melt thematrix material; applying the at least partially molten matrix materialand the particles of polycrystalline diamond material to the surface ofthe earth-boring tool; and allowing the at least partially molten matrixmaterial to cool and solidify on the surface of the earth-boring tool.13. The method of claim 1, wherein subjecting the diamond grains to thetemperature greater than about 1,500° C. and the pressure greater thanabout 5.0 GPa to form diamond-to-diamond bonds between the diamondgrains and faun, the polycrystalline diamond material comprises forminga layer of the polycrystalline diamond material.
 14. The method of claim13, wherein breaking down the polycrystalline diamond material to formparticles of polycrystalline diamond material comprises forming at leastsubstantially planar fragments of the layer of polycrystalline diamondmaterial.
 15. The method of claim 14, further comprising forming the atleast substantially planar fragments of the layer of polycrystallinediamond material to have an average particle diameter between about 0.25millimeter and about 7.0 millimeters, and an average particle thicknessbetween about 0.1 millimeter and about 5.0 millimeters.